The rapid growth of Internet services such as Web email, Web search, Web site hosting, and Web video sharing is creating increasingly high demand for computing and storage power from servers in data centers. While the performance of servers is improving, the power consumption of servers is also rising despite efforts in low power design of integrated circuits. For example, one of the most widely used server processors, AMD's Opteron processor, runs at up to 95 watts. Intel's Xeon server processor runs at between 110 and 165 watts. Processors are only part of a server, however; other parts in a server such as storage devices consume additional power.
Servers are typically placed in racks in a data center. There are a variety of physical configurations for racks. A typical rack configuration includes mounting rails to which multiple units of equipment, such as server blades, are mounted and stacked vertically within the rack. One of the most widely used 19-inch rack is a standardized system for mounting equipment such as 1U or 2U servers. One rack unit on this type of rack typically is 1.75 inches high and 19 inches wide. A rack-mounted unit (RMU) server that can be installed in one rack unit is commonly designated as a 1U server. In data centers, a standard rack is usually densely populated with servers, storage devices, switches, and/or telecommunications equipment. In some data centers, fanless RMU servers are used to increase density and to reduce noise.
A data center room should be maintained at acceptable temperatures and humidity for reliable operation of the servers, especially for fanless servers. The power consumption of a rack densely stacked with servers powered by Opteron or Xeon processors may be between 7,000 and 15,000 watts. As a result, server racks can produce very concentrated heat loads. The heat dissipated by the servers in the racks is exhausted to the data center room. The heat collectively generated by densely populated racks can have an adverse effect on the performance and reliability of the equipment in the racks, since they rely on the surrounding air for cooling. Accordingly, heating, ventilation, air conditioning (HVAC) systems are often an important part of the design of an efficient data center.
A typical data center consumes 10 to 40 megawatts of power. The majority of energy consumption is divided between the operation of servers and HVAC systems. HVAC systems have been estimated to account for between 25 to 40 percent of power use in data centers. For a data center that consumes 40 megawatts of power, the HVAC systems may consume 10 to 16 megawatts of power. Significant cost savings can be achieved by utilizing efficient cooling systems and methods that reduce energy use. For example, reducing the power consumption of HVAC systems from 25 percent to 10 percent of power used in data centers translates to a saving of 6 megawatts of power which is enough to power thousands of residential homes.
In a data center room, server racks are typically laid out in rows with alternating cold and hot aisles between them. All servers are installed into the racks to achieve a front-to-back airflow pattern that draws conditioned air in from the cold rows, located in front of the rack, and ejects heat out through the hot rows behind the racks. A raised floor room design is commonly used to accommodate an underfloor air distribution system, where cooled air is supplied through vents in the raised floor along the cold aisles.
An important factor in efficient cooling of data center is to manage the air flow and circulation inside a data center. Computer Room Air Conditioners (CRAC) units supply cold air through floor tiles including vents between the racks. In addition to servers, CRAC units consume significant amounts of power as well. One CRAC unit may have up to three 5 horsepower motors and up to 150 CRAC units may be needed to cool a data center. The CRAC units collectively consume significant amounts of power in a data center. For example, in a data center room with hot and cold row configuration, hot air from the hot rows is moved out of the hot row and circulated to the CRAC units. The CRAC units cool the air. Fans powered by the motors of the CRAC units supply the cooled air to an underfloor plenum defined by the raised sub-floor. The pressure created by driving the cooled air into the underfloor plenum drives the cooled air upwardly through vents in the subfloor, supplying it to the cold aisles where the server racks are facing. To achieve a sufficient air flow rate, hundreds of powerful CRAC units may be installed throughout a typical data center room. However, since CRAC units are generally installed at the corners of the data center room, their ability to efficiently increase air flow rate is negatively impacted. The cost of building a raised floor generally is high and the cooling efficiency generally is low due to inefficient air movement inside the data center room. In addition, the location of the floor vents requires careful planning throughout the design and construction of the data center to prevent short circuiting of supply air. Removing tiles to fix hot spots can cause problems throughout the system.